Scope, architecture, and validation¶

Package structure¶

The distribution is pystac-ext-vcs; import the wrapper from pystac.extensions.vcs. The wheel excludes the shared namespace initializer owned by PySTAC.

VcsExtension uses PySTAC's PropertiesExtension and ExtensionManagementMixin. It wraps existing metadata dictionaries in place, preserving normal PySTAC serialization and cloning. No separate schema model or generated data class is needed. The authoritative contract remains the published VCS v0.1.0 JSON Schema.

VCS_EXTENSION_HOOKS identifies the schema and the Catalog, Collection, and Item object types. There are no previous extension identifiers. The package does not automatically register migration hooks or an .ext.vcs accessor.

Validation boundaries¶

Property assignments, apply(), and serialization do not run JSON Schema validation. apply() updates fields sequentially and clears omitted values. It does not create repository links or resolve branches and tags.

Install pystac[validation] and call the owning STAC object's validate() to check the complete document. Schema retrieval may require network access or an application-configured schema cache. Tests cache the unmodified published extension schema locally and validate its contract without network access.

The schema permits absent fields but rejects nulls, empty strings, non-string values, and unknown vcs: keys in its defined field locations. The prose specification additionally asks for at least one field; see the field reference.